There is known a pneumatic tire having a tread pattern of a so-called pitch variation in which a plurality of kinds of pattern-constituting units having different pitches (e.g., one lateral groove and one block which is adjacent to the lateral groove) in a circumferential direction of the tire are arranged at random in the tire circumferential direction (see Patent Document 1, for example). The tire of this kind disperses, in a wide range, frequency of pitch noise generated when a tread portion repeatedly comes into contact with a road surface during running, thereby enhancing the noise performance.    [Patent Document 1] Japanese Patent Application Publication No. 2006-176079